The present invention relates generally to electronic navigation devices and more particularly to a passive airborne radio navigation device, which automatically, and sequentially scans a plurality of VOR frequency channels, and simultaneously displays corresponding course bearing information on one or a plurality of digital indicators.
There is a vast body of knowledge relating to radio navigation devices including radio direction finders, radio ranges such as the four course radio range, VHF omni-directional range often in conjunction with a Tacan feature, as well as the several hyperbolic navigational systems such as the Loran system. While not limited thereto, the present invention finds particular utility in conjunction with the VHF omni-directional range commonly found in the Continental United States, and not requiring the distance measuring features sometimes associated with the VOR system.
Navigation VOR receivers capable of tuning the VOR frequency band between 108 and 118 megahertz are well known and are typically capable of tuning but a single channel at a time with each receiver including a single course deviation indicator and omni bearing selector display arrangement. In order to simultaneously monitor two or more VOR signals, the typical installation employs separate VOR receivers for each desired channel and the corresponding course bearing indicator for each receiver. Thus, a typical aircraft installation will include 2 independent VOR receivers which the pilot must periodically update during a cross-country flight.
Area navigation systems have become increasingly popular over the last several years. Such area navigation systems are typified by U.S. Pat. Nos. 3,750,942 and 4,069,412, and require a VOR receiver and a distance measuring equipment unit. Distance measuring equipment or DME is operable with only a fraction of the nationwide VOR navigational facility network and requires an airborne interrogator or transmitter and a ground based transponder which replies to interrogations from the airborne interrogator, returning pulses thereto for distance measuring purposes. In addition to being expensive and slow (often 20 seconds is required to determine an accurate distance from the aircraft to the navigational facility), such distance measuring equipment is not operable in conjunction with many of the VOR facilities which lack the transponder or Tacan capability. With the known area navigation systems, a way point omni bearing selector or OBS is used to set the proper bearing or azimuth and the DME feature provides a distance indication which may then be entered into a computation to determine a distance from a selected way point. Thus, in the prior art area navigation systems, an expensive and unreliable DME was used in conjunction with a one channel at a time VOR receiver to produce a desired way point. Such systems have been entirely manually operated requiring some time for the pilot to set up frequency and radial information to verify the proper identification of the VOR station, set up the distance measuring equipment, and then navigate to the desired way point. It is estimated that only two thirds of the VOR stations in the Continental United States provide the necessary DME information for such navigation.